[TowerTalk] N - clamp style connector

Wed Mar 10 18:25:54 PST 2010


Steve Katz wrote:
> Well, you've certainly had some experiences there with wild WX!
>
> I've never seen the silver plating actually come off a good N connector, but then I've also never taken any direct lightning hits, either.  Maybe the huge surge of energy boils off the plating or something, I'm not a metallurgist; but I would *think* that if the plating comes off, it has to redeposit somewhere else.  The plating is only microinches, so there isn't a lot of it to begin with.
>
> However, in 45 years of doing antenna work, I've never seen an unprotected and properly installed N connection or splice go bad outdoors, and I've never seen the plating "disappear."  I've seen it turn black hundreds of times, but normally the oxide protects the base metal very well.
>   
Actually these I'm describing didn't go bad. They'd have passed all 
those tests. They just wouldn't come apart.
As to the silver plating, all I can do is guess, and that's one of the 
few things I don't have any photos of.  "I'd guess" that the coronal 
discharge vaporized the silver, hence the dull, or sand blasted like 
finish on the brass (and nearly every thing else up there except the 
antennas), and in the wind the vaporized silver just blew away.

Our astronomy club used to silver and aluminumize  mirrors using a 
coronal discharge to vaporize either Aluminum or Silver in a vacuum. The 
metal then deposited on the mirror's surface.
> I guess we all go by what we've dealt with; but I've had great luck using N fittings outdoors, completely unprotected, and never had one go bad in four and a half decades.
I wrap them, or more often put flooded heat shrink over them, but their 
reliability is one of the reasons I went to them. Unfortunately I've 
blown up a few on 75 and 160 with the very high voltages when operating 
at the band edges at the legal limit and resultant high SWR.  After they 
fail like that, they check good, but show a high SWR when power is 
applied. I've never hy-potted one of those that had failed, but I'd bet 
they would not pass that test.

73

Roger (K8RI)
>   After assembly we did only three tests on military cable assemblies, under contract from the DoD: (1) Mechanical pull test, it had to pass 60 lbs dead hang for 60 seconds; (2) Hipot test, it had to pass 2500Vdc with a trip point of 100uA; (3) VSWR test, the assembly had to provide >30 dB return loss (when terminated in a standard and rather perfect load) at 100 MHz for cables exhibiting <1 dB loss, or 33 dB for cables exhibiting <3 dB loss at 100 MHz.  That's all we were required to do, and we'd get >95% yields, actually very close to 100% on most lots, making thousands of cable assemblies.
>
> 73 de Steve WB2WIK/6
>
>
>
> -----Original Message-----
> From: towertalk-bounces at contesting.com on behalf of Roger (K8RI)
> Sent: Wed 3/10/2010 4:16 PM
> To: Tower and HF antenna construction topics.
> Cc: w4lde at numail.org
> Subject: Re: [TowerTalk] N - clamp style connector
>  
>
>
> Steve Katz wrote:
>   
>> K8RI: I'm pretty sure those are the ones that turn a rough, dusty,
>> bluish 
>> green around here. Nickel plate is terrible and silver just disappears.
>>
>> That's the main reason I never worry about turning connectors into 
>> permanent attachments and use the flooded heat shrink.  IT also keeps 
>> them nice and clean. 
>>
>> WB2WIK: You know, it's not what the outside of the connector looks like
>> that's important.  It's what happens inside.  Using silver-plated,
>> mil-spec UG-21D/U type N connectors, I've used them outdoors, completely
>> unprotected, for years and years and years even at the seaside when I
>> lived on the ocean in central NJ.  The outsides turn very "black" in
>> color, but the silver doesn't disappear -- it just develops an oxide
>> coat, which actually protects the connector as soon as it happens.
>>   
>>     
> I don't worry about them while they're "up there", but normally these 
> refuse to come apart with the nut becoming a permanent part of the body 
> on the shiny ones.  All of the silver plated ones, at least on top of 
> the tower end up with no plating left. They are just green brass. IF 
> they come apart they squeal as the nut is turned out taking a good 
> portion of the threads with them.  I normally use "N-type" for the 
> weather proofing as most of the external stuff is gone within a year or 
> two and bare UHF connectors provide no weather proofing. The MMM flooded 
> heat shrink is about the only stuff that has managed to stay, but it 
> hasn't had a real work out with lightning.  The first 5 years the tower 
> took 3 visually verified, direct hits each year. It's only taken two 
> since then. How many unverified hits? Who knows, but I thought for a 
> while I had a lightning magnet.  Since installing the elaborate ground 
> system and grounding the coax shield at the top and bottom of the tower 
> I've had no damage to any equipment or coax even with all those hits. 
> Connectors "up there" look pretty ratty but are still working.
>
> BTW, after one storm I found some large pieces of tape and coax seal in 
> the yard. They looked a lot like expanded metal. So tape and seal in 
> hand, or rather, pocket I headed up the tower.  There I found all of the 
> connectors were bare metal. Most were clean brass that appeared to be 
> etched, but absolutely no silver plate left on N or UHF. IIRC I had to 
> throw away one of the UHF connectors as it had to be cut off the coax.  
> I couldn't get them apart. At least I didn't find any water in the 
> coax.  I replaced the coax seal and tape.  They were still working about 
> 7 years later when the new tower went up.
>
> Oh! a while back I had to get started on replacing the pigtails at the 
> top.  Only one connector out of the 5 cables would come apart. I had to 
> cut all of the others off and no these were not filled with epoxy<:-)) 
> But they were thoroughly weatherproofed with the MMM heat shrink.  All 
> connectors were still shiny, but  neither UHF nor N would budge.  I 
> didn't cut any of them apart, but they acted like the threads were 
> welded...or gauled(sp?).
>
> 73
>
> Roger (K8RI)
>
>
>   
>> After several years of direct exposure I've unscrewed these fittings and
>> found everything underneath to be shiny and dry.  I've absolutely never
>> seen one take in a drop of water (unprotected) if it's the right
>> connector, installed on the right cable, so they are compatible.  
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